For example, there has been used a technique for, in a parallel-type chiller in which two compressors are associated with one heat exchanger to constitute a chiller cycle, reducing the compression ratio of the compressors to improve efficiency by positioning an evaporator and a condenser in an one-pass countercurrent arrangement, partitioning a refrigeration system at a longitudinal-direction mid-position (middle) of each of the evaporator and the condenser to divide each of the evaporator and the condenser into a low-pressure side and a high-pressure side, and connecting the divided low-pressure sides and high-pressure sides to the compressors, respectively (for example, see Patent Literature 1). Since the parallel-type chiller provided with multiple compressors as described above can show a cooling capacity corresponding to the number of compressors, it is expected to perform individual control of the compressors, such as capacity control of each compressor and rotation speed control in the case where an inverter is used.
Patent Literature 2 proposes a technique for, when a cooling capacity changes, controlling an inverter operating compressors, by rotation speed determined on the basis of a first parameter reflecting refrigerant (gas) flow based on the quantity of output heat of a chiller and a second parameter reflecting a head based on evaporator pressure and condenser pressure to stably and efficiently operate a turbo chiller.